The Alternative Fuels SUPPLY system contains the following components:

Fuel Tank

The CNG Fuel Tank is constructed of steel and is wrapped in carbon fiber set in epoxy. The high pressure lock-off solenoid is contained within the fuel tank and is used to prevent fuel flow during non-cranking or running engine conditions. Storage capacity of the tank varies with vehicle model. Refer to the owners manual supplement for storage capacity. Fuel tanks have a protective cover. The cover is designed to protect the tank from damage due to shifting cargo and also for ultra-violet (UV) radiation protection in pick-up truck applications. Regulations require that the fuel tank and brackets be inspected every three years or 60,000 km (36,000 mi) , which-ever comes first. Fuel tank inspection results should be recorded in the CNG Fuel Tank Inspection Record area of the owners manual supplement. The service life of the CNG fuel tank is 15 years from the date of manufacture. All CNG fuel tanks regardless of inspection results must be replaced after  15 years. Refer to Fuel Tank Inspection procedures.

Fill Valve and Fill Line

The fill valve receives fuel from the fill nozzle at the CNG dispensing station. The fill valve seals to the dispensing nozzle with an O-ring. Before re-fueling this O-ring must be inspected and replaced if missing or damaged. The fill valve contains an internal 380 micron filter element designed to trap contaminants. This filter must be periodically inspected and cleaned. Refer to Fill Valve Filter Replacement for filter inspection and cleaning procedures. The fill valve mounting location varies with vehicle model. Refer to the owners manual supplement for fill valve location and fuel tank filling procedures. The fill line is constructed of flexible, steel-braided hose protected by a plastic cover. The fill line connects the fill valve to the fuel tank and is sealed to the fuel tank with an O-ring.

Fill Line Union Check Valve

The fill line is equipped with a check valve. In the event of fill valve leakage, the check valve is designed to minimize the amount of CNG fuel leakage. The check valve must be installed with the flow direction arrow pointed towards the high pressure lock-off solenoid.

High Pressure Lock-Off (HPL) Solenoid

The HPL is a normally closed, solenoid valve. The HPL solenoid and a low pressure lock-off (LPL) solenoid in the fuel line prevent fuel flow. The alternative fuels engine control module (AF ECM) commands ONLY the HPL open for 1 second at EVERY ignition ON for a CNG prime pulse. The CNG prime pulse is performed in order to charge the fuel line and also allows the fuel tank pressure (FTP) sensor to monitor the amount of fuel pressure in the tank. The AF ECM commands BOTH the HPL and the LPL open when engine RPM indicates the engine is cranking or running on CNG.

Fuel Tank Pressure (FTP) Sensor

The FTP sensor is a pressure transducer. The AF ECM supplies about 5 volts on the FTP sensor reference circuit. The AF ECM also supplies a signal and ground circuit to the FTP sensor. Located at the end of the fuel tank, threaded into the HPL, the FTP sensor supplies a voltage signal to the AF ECM. With a full fuel tank a high voltage signal will be monitored by the AF ECM. The volume of CNG varies with temperature and pressure. This will vary the amount of fuel vs. the signal voltage the FTP sensor supplies to the AF ECM. In order to compensate for the different voltage factors, a tank mounted -- internal -- fuel tank temperature (FTT) sensor is also monitored by the AF ECM. The AF ECM performs a calculation on the FTP sensor voltage vs. the in-tank temperature. The AF ECM will then control the fuel gage to display the correct fuel level.

Fuel Tank Temperature (FTT) Sensor

The FTT sensor is a thermistor mounted inside the HPL and is not serviceable separately from the HPL. The FTT thermistor has high resistance when cold and low resistance when hot. The AF ECM supplies about 5 volts to the FTT sensor signal circuit. When FTT sensor resistance is high -- cold sensor-- the FTT sensor signal voltage is high. As the FTT sensor warms and resistance drops, less signal voltage is monitored by the AF ECM. The volume of CNG varies with temperature and pressure. This will vary the amount of fuel vs. the signal voltage the FTP sensor supplies to the AF ECM. In order to compensate for the different voltage factors, a tank mounted -- internal -- fuel tank temperature (FTT) sensor is also monitored by the AF ECM. The AF ECM performs a calculation on the FTP sensor voltage vs. the in-tank temperature. The AF ECM will then control the fuel gage to display the correct fuel level.

High Pressure Line

The high pressure line is stainless steel tubing with matching high pressure O-ring face seal (ORFS) fittings. The individual tubes are pre-formed with fittings installed. All O-ring face seal fittings use nitrile rubber O-rings and might be identified with a yellow or white band. These O-rings must be replaced with the correct replacement part whenever a line is opened.

When installing NPT -- pipe thread -- fittings DO NOT use Teflon® tape. Tape fragments could lodge in a regulator and allow fuel pressure to exceed specified levels. The use of pipe sealant with Teflon® is required.

Intermediate Pressure Fuel Hose

The intermediate pressure fuel hose assembly is a unique two-piece stainless steel braided hose and is designed to isolate AF components from vibration.

Low Pressure Hose

Low pressure gas is supplied to the gas mass sensor / mixture control valve (GMS / MCV) and also to the gas distribution adaptor (GDA) with Gann®  VH-100 vapor hose. This hose is a patented non-permeable hose.

The Alternative Fuels METERING system contains the following components:

High Pressure Regulator (HPR)

The HPR is supplied with fuel from the CNG fuel tank at up to 3600 psi (24821 kPa) through high pressure stainless steel lines. The HPR reduces fuel pressure to between 115-220 psi (793-1517 kPa). The outlet of the HPR is the Intermediate pressure stage. Fuel flows out of the HPR and into the low pressure lock-off (LPL) solenoid. The pressure drop within the regulator causes fuel temperature to drop. In order to prevent HPR freeze-up, the HPR is connected to the vehicle engine cooling system. The HPR contains an over-pressure relief device (PRD) which will not allow pressure above 400 psi (2758 kPa) on the output stage of the HPR. The PRD is removable in order to allow the installation of a pressure gauge for diagnostic purposes. The HPR has an internal, serviceable 40 micron filter. This filter must be serviced periodically. Refer to High Pressure Regulator Filter Replacement in this supplement for service intervals.

Low Pressure Lock-Off (LPL) solenoid

The LPL is a normally closed, solenoid valve. The LPL is mounted in the Intermediate pressure line. The AF ECM controls LPL solenoid operation. The AF ECM energizes the LPL solenoid only when engine cranking or running is detected. Anytime the engine is stopped the AF ECM de-energizes the LPL solenoid which stops fuel flow. The AF ECM operates the LPL and the high pressure lock-off (HPL) solenoid at the same time except at ignition ON. During ignition ON only the HPL is opened while the LPL remains closed in order to charge the fuel system with CNG. The LPL is supplied fuel from the HPR with fuel pressure between 115-220 psi (793-1517 kPa). The outlet of the LPL supplies the low pressure regulator (LPR) with fuel.

Low Pressure Regulator (LPR)

The low pressure regulator (LPR) is a two stage regulator. The fuel enters the LPR at the intermediate stage pressure of 115 to 220 psi (793-1517 kPa). The first -- primary -- stage of LPR operation reduces the fuel pressure down to between 4-6 psi (28-41 kPa). The fuel pressure is then again reduced in the second -- secondary -- stage of the LPR down to between 2-5 inches (5.1-12.7 cm) of water column or around 0.21 psi (1.5 kPa ). The fuel exits the LPR and flows through the low pressure hose and into the gas mass sensor/mixture control valve (GMS/MCV). The LPR contains two 1/8 in (3.175 mm) NPT test ports with plugs. The plugs are removable in order to allow the installation of a pressure gage for diagnostic purposes. One port tests the first (primary) stage and the other port tests the second (secondary) stage. Refer to Fuel System Diagnosis for pressure checking procedures.

Gas Mass Sensor/Mixture Control Valve (GMS/MCV)

The GMS/MCV combines a hot wire type anemometer (GMS) and a magnetic rotary valve (MCV) into one non-serviceable unit. The GMS/MCV is mounted in the low pressure hose between the low pressure regulator (LPR) and the gas distribution adaptor (GDA). The GMS measures the mass fuel flow and outputs a frequency signal to the AF ECM. The AF ECM process this signal to determine the amount of fuel entering the engine. The AF ECM compares the GMS information as well as the information of other engine sensors and determines an optimum fuel flow rate to maintain a stoichiometric air/fuel ratio of 16.5 to 1. In order to change the fuel mixture rich or lean, the AF ECM modulates the MCV. The MCV will then allow less or more fuel into the engine.

Gas Distribution Adaptor (GDA)

The gas distribution adaptor (GDA) replaces the gasoline only air inlet duct. The GDA houses a gas ring which has distribution slots. The slots allow the CNG fuel to mix evenly into the intake air stream.

This vehicles primary fuel source is compressed natural gas (CNG). The vehicle will only switch-over to gasoline operation if one of the following conditions is present:

60 Day Cycle

It is recommended that every 60 days the vehicle be cycled between CNG and gasoline. This ensures the gasoline fuel system stays in good working condition and also accommodates for seasonal changes in gasoline formulation. Perform the following steps every 60 days.

1. With the vehicle operating on CNG check the gasoline level, fill if needed.
2. Operate the vehicle until the CNG fuel tank is empty and the vehicle switches over to gasoline operation.
3. Operate the vehicle until the gasoline tank is near empty.
4. Refill both fuel tanks.
5. The vehicle will switch-over to CNG operation.
6. Repeat procedure in 60 days.

Fuel Indicator Lamp (FIL)

The fuel indicator lamp (FIL) is contained within the fuel gauge selector switch button. The fuel indicator lamp indicates which fuel system is in operation. The AF ECM controls the operation of the fuel indicator lamp. The fuel indicator lamp illuminates ONLY when the engine is operating on gasoline. The fuel indicator lamp will also illuminate for several seconds during start-up as a bulb check.

Fuel Gage Operation

The instrument panel fuel gage displays the level of the fuel system that is operating the engine until the operator of the vehicle requests the non-operating fuel system level to be displayed. Once requested, the non-operating fuel system level will be displayed for about 10 seconds. The Bi-fuel CNG fuel gage system utilizes a fuel gage selector switch and a fuel gage relay. This allows the two different fuel tank level readings (CNG and gasoline) to be displayed by the one instrument panel fuel gage. The fuel gage selector switch is a momentary-closed type switch located within reach of the vehicle operator. The fuel gage switch allows the vehicle operator to observe the fuel level of each fuel system regardless of which fuel system is currently in operation. The AF ECM monitors the status of the switch. When the switch is depressed the AF ECM commands the fuel gage relay either ON or OFF depending on which fuel system is in operation. The fuel gage relay allows either the fuel level from the gasoline tank or the fuel level of the AF ECM to be monitored by the PCM. The CNG fuel level is determined by the AF ECM. The AF ECM monitors the fuel tank pressure and fuel tank temperature sensors that are located at the CNG tank HPL. The AF ECM performs a calculation of the CNG pressure and CNG temperature. The AF ECM generates a pulse width modulated signal that can be monitored by the PCM. The PCM then sends the fuel level information to the instrument panel using Class 2 serial data. Passenger vehicles have a filtered fuel level display, depress the fuel gage select switch 30 seconds after the vehicle speed sensor indicates the vehicle is at rest in order to avoid inaccurate gage displays.

The AF ECM controls the fuel system while the vehicle is operating on CNG. The AF ECM receives signals from various engine sensors and determines the correct amount of fuel required by the engine. The fuel is stored in a cylindrical fuel tank. A full tank can contain fuel at 3600 psi (24,820 kPa). A high pressure lock-off (HPL) solenoid in the tank and a low pressure lock-off (LPL) solenoid in the fuel line prevents fuel flow until the AF ECM monitors that the engine is cranking or running. This fuel delivery system utilizes three different pressure stages in order to lower the fuel pressure from tank pressure down to a delivery pressure which is slightly above atmospheric pressure.

High Pressure (tank) Stage

When the AF ECM commands the HPL open fuel begins to flow at up to 3600 psi through the high pressure steel lines up to the high pressure regulator (HPR). The HPR reduces fuel pressure to between 115-220 psi (793-1517 kPa). The outlet of the HPR is the Intermediate pressure stage. The pressure drop within the regulator also causes fuel temperature to drop. In order to prevent HPR freeze-up, the HPR is connected to the vehicle engine cooling system.

Intermediate Pressure Stage

The Intermediate Pressure Stage begins at the outlet of the high pressure regulator (HPR). With a pressure between 115-220 psi (793-1517 kPa), the fuel exiting the HPR flows through the intermediate fuel line to the low pressure lock-off (LPL) solenoid. The LPL is controlled by the AF ECM. Fuel flows out of the LPL through another portion of Intermediate fuel line and into the low pressure regulator (LPR). The inlet of the LPR is the Low Pressure Stage.

Low Pressure Stage

The low pressure regulator (LPR) is a two stage regulator. The fuel enters the LPR at the intermediate stage pressure of 115-220 psi (793-1517 kPa). The first stage of LPR operation reduces the fuel pressure down to between 4 and 6 psi (28-41 kPa). The fuel pressure is then again reduced in the second stage of the LPR down to between 2-5 inches (5.1-12.7 cm) of water column. The fuel exits the LPR and flows through the low pressure hose and into the gas mass sensor / mixture control valve (GMS / MCV). The AF ECM monitors the gas mass sensor information and adjusts the amount of fuel entering the engine by varying fuel flow through the mixture control valve. The fuel exits the GMS/MCV and flows through another portion of low pressure hose and into the gas distribution adaptor (GDA). The fuel mixes with inlet air and is drawn through the intake manifold to be burned by the engine.